The present invention relates generally to the field of electronic microcircuit fabrication and, more particularly, to a process of fabricating a metallurgically enhanced heat sink.
A typical microelectronic package includes an integrated circuit device (e.g., a silicon chip) mounted to a carrier substrate with an epoxy-based material disposed between the die and the substrate. A heat sink (e.g., aluminum or copper) is generally included in the package and has direct contact with the die so that heat generated by the die can dissipate by convection directly into the surrounding air.
However, as the industry moves towards faster and smaller microelectronic devices, effective heat management is becoming more difficult. For example, the miniaturization of microelectronic devices involves not only crowding an increasing number of circuits on to a single chip, but also reducing the overall chip package size. Although smaller devices are necessary for certain high-performance applications (e.g., hand-held computers, portable telecommunications equipment, and the like) these devices tend to generate more heat due to a higher integration of circuits. One problem associated with ineffective thermal management can cause the central portion of a die, secured to a substrate, to curve or bend. This may cause some of the electrical connections between the die and the substrate to separate. Another damaging effect caused by thermally induced curving includes cracking and/or breaking of the die. In this instance, tensile stresses occur in the outer layer of the die as it bends. If these stresses are greater than the fracture strength of the die, it chips or breaks. Moreover, as the temperature becomes very hot, the inner dielectric layer may melt and cut off the electrical connection leading to total failure of the device.
One method of solving this problem has been to make heat sinks more efficient. For example, by reducing the thermal resistance between the heat sink and the die (i.e., by using a heat conductive adhesive such as grease, phase changing material, or solder alloy to attach the die to the heat sink) the heat transfer process is improved. Another technique has been to fabricate heat sinks from materials such as kovar or other expensive alloys with higher thermal conductivity than more conventional materials such as aluminum and copper. Nevertheless, alloys such as kovar do not provide a cost effective packaging solution.
As the advances in microelectronic fabrication continue to yield even more densely packaged high power transistors that are operated at faster and faster clock speeds, the problems associated with heat generation and heat dissipation will only become more acute. Therefore, it would be advantageous to enhance the thermal conductivity of heat sinks.